This invention relates to the field of wireless communication, and more specifically to the construction of planar inverted-F antennas (PIFAs) for use in wireless communication devices such as mobile telephone handsets.
The Advanced Mobile Phone Service (AMPS) and the Personal Communication Service (PCS) frequency bands, and the Global System for Mobile Communications (GSM) and the Digital Cellular System (DCS) frequency bands, form the basic dual cellular frequency bands within the US and within Europe, respectively.
There is a demand for wireless communication devices that will accommodate both the US AMPS/PCS frequency bands and the European GSM/DCS frequency bands within a single wireless communications device, so that a single wireless communications device, such as a cellular handset, can be used worldwide. This evolution toward a single cellular handset having global utility results in a need for cellular antennas that will simultaneously cover the AMPS/PCS/GSM/DCS frequency bands.
In addition, use of an antenna that is buried within, or is internal to, a cellular handset is desirable. Among the choices for an internal antenna for use within cellular handsets, a PIFA is very versatile in terms of its physical size and its performance.
In the past, multi-band PIFAs (for example two band or three band) have been provided having two or more RF feeds. However multi-feed PIFAs encounter disadvantages such as increased cost and increased mutual coupling that results from poor isolation.
Extension of a multi-feed multi-band PIFA in order to provide a global cellular PIFA (i.e. a PIFA that covers the AMPS/PCS/GSM/DCS frequency bands), cannot easily be accomplished due to the fact that the lower cellular frequency bands AMPS and GSM are close to each other, and in fact they have a region of frequency overlap, and the same is true for the upper frequency cellular bands DCS and PCS. Due to this close frequency proximity of the relevant frequency bands, as well as the region of frequency overlap, the use of two PIFAs that operate separately in the AMPS/PCS frequency bands and the GSM/DCS frequency bands can be provided within a cellular handset. But this two-PIFA assembly requires that the two antennas occupy about twice the physical volume within a cellular handset that a single PIFA would require. In addition, partitioning the physical antenna-volume that is normally available within a practical and realistic cellular handset does not usually provide a desired separate resonance in both the AMPS frequency band and the GSM frequency band. Even if one were to succeed using such a two-PIFA design, providing adequate isolation between the two PIFAs is difficult. In view of these practical design constraints, the use of two PIFAs, having two feeds and having multiple frequency bands, is not a logical choice for the realization of a global cellular PIFA construction and arrangement.
Progress has been made in the cellular technology to provide a single-feed two-band PIFA. There also has been progress in the bandwidth enhancement of single feed two-band and three-band PIFAs.
Prior art PIFAs include a radiating/receiving element (hereinafter called a radiating element) having a length and a width that is optimized to approximate a quarter-wavelength within its semi perimeter. In order to reduce the resonant frequency of the PIFA without increasing its physical size, slots of different shapes have been used within the PIFA""s radiating element. With the judicious choice of a slot configuration, and by optimizing the position of the radiating element""s shorting post, PIFA designs have emerged for single-feed multi-band operation.
In prior art single-feed multi-band PIFAs, the multi-band operation is the result of a combination of the quasi physical partitioning of a single band PIFA""s radiating element, wherein the radiating element is a derivative of a corresponding single-feed, single-band, PIFA.
In prior art dual-feed multi-band PIFAs having two radiating elements, the two radiating elements are physically isolated from each other.
In multi purpose cellular handsets that are usable in both cellular and non-cellular applications, a multi-band antenna that simultaneously operates in both the cellular and the GPS/Bluetooth frequency bands is of interest, wherein Bluetooth (BT) is a code name for a proposed open specification to standardize data synchronization between disparate PC and handheld PC devices. Single-band PIFAs have proven to be useful in meeting the demand of GPS/BT applications.
In prior art designs, an internal GPS band antenna has been used along with a dual-band cellular antenna, to thereby provide a dual-feed, three-band, two-antenna assembly. Such dual-feed three-band two-antenna assemblies have to encounter design complexities in order to ensure adequate isolation between the two feed ports that support the two cellular frequencies and the GPS frequencies.
Conventionally, a single-feed dual-band PIFA requires only one shorting post. In the prior art, slots of different shapes have been used in the radiating element of a PIFA, mainly to lower the resonant frequency of the radiating element without increasing the physical size of the PIFA. Although attempts have been made to provide a three-band PIFA by improving the bandwidth of a two-band PIFA, little or no success has been achieved relative to providing a single-feed four-band PIFA, or in providing for a simultaneous non-cellular band (GPS/ISM) resonance within the same four-band PIFA.
In certain PIFA designs, parasitic elements have been used in a dual-band PIFA to generate an additional resonance for non-cellular application.
In order to meet the demand of a global cellular antenna, U.S. Pat. No. 6,255,994, provides for the multiple resonance of a PIFA by providing frequency-selecting switches for different resonant frequencies, so that the same telephone and antenna can be used globally. However, such a design results in an increased cost and additional complexities due to the increased number of electrical connections/components that are required for the antenna. In addition, and apart from the higher cost, the possibility exists for a gain degradation of the antenna when additional electrical components are introduced into the antenna.
This invention provides a single-feed four-band virtual two-PIFA assembly (hereinafter more conveniently called a two-PIFA assembly) that is responsive to the AMPS, PCS, GSM and DCS frequency bands, wherein this multi-band operation is realized by inserting the metal radiating element of one PIFA (i.e. an inner radiating element) within the metal radiating element of another PIFA (i.e. an outer radiating element).
A generally C-shaped slot separates the metal inner radiating element from the metal outer radiating element, and two spaced-apart metal stubs define the two ends of the C-shaped slot. That is, these two metal stubs are located in the discontinuity area of the C-shaped slot. These two metal stubs (the C-shaped slot""s discontinuity area) physically and electrically connect the inner radiating element to the outer radiating element.
Separate metal shorting posts are provided for each of the inner and outer radiating elements, to thereby connect both of these radiating elements to a metal ground plane element that is located under, and generally parallel to, a plane that contains the two radiating elements.
The non-radiating edge of the outer radiating element is electrically connected to a single feed post, and one of the two metal stubs that connect the outer radiating element to the inner radiating element is located relatively close to this feed post, to thus provide a virtual feed to the inner radiating element.
RF energy is fed to and taken from the two-PIFA assembly by way of this single feed post, wherein at least one of the two metal stubs acts as a virtual RF feed for the inner radiating element.
The outer radiating element, having the single RF feed post and a shorting post located on its non-radiating edge, acts as a first PIFA. The inner radiating element, the metal stub(s) that acts as a virtual RF feed thereto, and a second shorting post that is electrically connected to the ground plane element, acts as a second PIFA.
While two metal stubs are provided in embodiments of this invention, more generally a plurality of metal stubs connect the inner radiating element to the outer radiating element. With reference to the above-mentioned first PIFA and its outer radiating element, this plurality of metal stubs provide a matching and/or tuning function. With reference to above-mentioned second PIFA and its inner radiating element, this plurality of metal stubs provides both a virtual RF feed, and a matching/tuning function.
In addition, the present invention provides a generally L-shaped slot that is punched or cut into a metal sheet that contains the above mentioned C-shaped slot, inner radiating element and outer radiating element. This generally L-shaped slot has an open end that is located on the non-radiating edge of the outer radiating element, at a location that is between this element""s feed post and shorting post. This generally L-shaped slot provides a wide bandwidth and the desired dual resonant frequencies. This L-shaped slot on the outer radiating element results in the effective quasi physical partitioning of the outer radiating element, resulting in the dual resonant characteristics of that PIFA.
As above-described, two spaced-apart metal stubs connect the outer radiating element to the inner radiating element, and these two spaced-apart metal stubs terminate the two ends of the above-described C-shaped slot. That is, the placement-choice of these two metal stubs results in two separate slot-discontinuities in what would otherwise be a continuous slot that separates the inner and outer radiating elements.
The first metal stub slot-discontinuity that interrupts such a visualized continuous slot is preferably placed in close proximity to the feed post that is located on the non-radiating edge of the outer radiating element. The second metal stub slot-discontinuity in such a visualized continuous slot is placed in close proximity to the closed end of the L-shaped slot.
A virtual RF feed post for the inner radiating element is provided by way of the first slot-discontinuity (i.e. by the first metal stub) in the C-shaped slot, and the second slot-discontinuity (i.e. the second metal stub) in the C-shaped slot functions as a matching and/or tuning element for the inner radiating element. Thus, the first metal stub can be considered to be a virtual feed post for the inner radiating element, and the second metal stub can be considered to be a tuning/matching element for the inner radiating element.
In addition, and in view of the direct physical connection of the first and second metal stubs to the outer radiating element, the first and second metal stubs can be considered to be matching/tuning elements for the outer radiating element.
A single-feed multi-band two-PIFA assembly utilizing the xe2x80x9cPIFA within a PIFAxe2x80x9d construction and arrangement of the present invention also provides additional resonance in the GPS frequency band. Thus, the single-feed multi-band xe2x80x9cPIFA within a PIFAxe2x80x9d of the present invention finds utility in systems that simultaneously require cellular and non-cellular resonance.
This single-feed multi-band xe2x80x9cPIFA within a PIFAxe2x80x9d of this invention, having response in both cellular and non-cellular resonant frequency bands, is achieved by providing a composite radiating element having a generally C-shaped slot therein that divides the composite radiating element into an inner radiating element and an outer radiating element, to thus provide a single-feed multi-band two-PIFA-assembly construction and arrangement for global cellular communications, including the AMPS/GSM/DCS/PCS frequency bands.
The construction and arrangement of this invention provides a xe2x80x9cPIFA within a PIFAxe2x80x9d wherein the radiating element of one PIFA is inserted into the radiating element of another PIFA. The quasi physical separation that exists between these two radiating elements provides for very nearly independent control of the multiple resonant frequency bands of the two individual PIFAs that are within the two-PIFA assembly.
The combination of, and the physical location of, the generally L-shaped slot and the generally C-shaped slot, along with the two metal stubs that connect these two slots, facilitates tuning the resonant frequencies of the two-PIFA assembly to the desired frequency bands.
The physical position of a single feed post, the size and position of a first shorting post for the outer radiating element, the size and position of the metal stub that acts as a virtual feed for the inner radiating element, the size and position of a second shorting post for the inner radiating element, as well as the size and position of the metal stub(s) that act as a matching/tuning element for the inner radiating element, the position and dimensions of the L-shaped slot on the outer radiating element, and the position and the dimensions of the C-shaped slot on the inner radiating element, provide an impedance match for the multi-band performance of the two-PIFA assembly, wherein multi-band impedance matching is achieved without the need for an external matching network.
Single-feed multi-band two-PIFA assemblies in accordance with the present invention provide resonant frequencies having utility in both cellular and non-cellular applications, wherein a single, unitary, two-PIFA assembly provides a xe2x80x9cPIFA-within-a PIFAxe2x80x9d construction and arrangement, and wherein it is relative ease to control the resonant characteristics of the two-antenna assembly so that the assembly in accordance with this invention exhibits resonance performance that is adequate for global cellular communication, including the AMPS/GSM/DCS/PCS frequency bands, without requiring a switch or an external matching network.
From the structural point of view, multi-band two-PIFA assemblies in accordance with the invention require only that an additional shorting post be provided for the inner radiating element, and the composite radiating element of the multi band two-PIFA assembly is amenable for large-scale manufacturing by punching/cutting, and then bending, a single piece of metal.
In accordance with a feature of this invention, a single metal sheet or plate is punched or cut in order to provided (1) a generally C-shaped slot that separates the metal sheet into an inner radiating element and an outer radiating element, (2) an L-shaped slot and a linear slot that are associated with the two radiating elements, (3) at least two metal stubs that interrupt the generally C-shaped slot and structurally support the inner radiating element in a cantilever fashion, (4) a metal shorting post for connecting the outer radiating element to a ground plane, (5) a metal feed post for transmitting RF energy to and from the outer radiating element, and (5) a plurality (for example three) metal plates that are connected to the edges of the outer radiating element.
Single-feed multi-band two-PIFA assemblies in accordance with the invention resonate in the AMPS/PCS frequency bands and the GSM/DCS frequency bands, as well as in the GPS frequency band, and they provide great potential for utility in global cellular handsets and in system applications that require simultaneous cellular and non-cellular operation.
Many original equipment manufacturers (OEMs) desire a cellular antenna, and more specifically an internal cellular antenna, that operates in both the US cellular (AMPS/PCS) and the European cellular (GSM/DCS) bands. The single-feed multi-band two-PIFA assembly of this invention, having four band (AMPS/GSM/DCS/PCS) performance, is an appropriate choice for these OEMs. In view of an additional resonance in the non-cellular (GPS) frequency band, the multi-band two-PIFA assemblies of this invention have additional utility in systems requiring simultaneous cellular and non-cellular operations.